The present invention relates to the foundry art and more particularly to casting utilizing a unique composite core assembly.
Castings that exhibit numerous cavities and passageways often are difficult to cast due to the complex core arrangement necessitated by the geometry of the casting. For example, engine cylinder heads require water jacket passages and gas ports which has necessitated the handling and assembling of numerous cores. Often, some assemblies were pasted or glued together in order to complete the core assembly in the core box. Such gluing technique was found to be unsatisfactory due to the tendency of the casting to contain unwanted fins and like defective areas.
Another problem associated with such castings was the need for providing wall sections of varying thickness within the interior of the casting. Thin wall sections can be difficult to achieve as those knowledgeable in the foundry art will appreciate.
An apparent solution to the foregoing problems is proposed in U.S. Pat. No. 4,462,453 and U.S. Reissue No. 31,488. The '488 reissue patent proposes a composite core assembly wherein conventional casting cores are placed in intimate contact with temporary cores molded from a destructable cellular plastic material typified by polystyrene and various methacrylic acid-based polymers. The plastic cores were molded to the desired shape of the metal casting itself while the conventional casting cores were intended to occupy the voids or empty cavities within the casting. After the composite core assembly was set in the casting box and the cope and drag sections united, molten metal would be poured into the core box resulting in the destruction of the plastic core by the hot metal. Resulting vaporous material from the plastic core would be vented by the conventional venting system provided in the core box.
One of the problems plaguing such a proposal was the inability for complete removal of gaseous by-products resulting from the plastic core. The '453 patent proposed to solve such problems by dissolving the polystyrene or other plastic material forming the temporary core utilizing aromatic or halogenated hydrocarbon solvents, including benzene, toluene, 1-1-1-trichloroethane, and the like. After the solvation of the plastic core, the casting operation could proceed as normal.
Deficiencies in the solvent dissolving process include the use of solvents which are expensive, require exposure limits, and cause dissolved plastic to penetrate into the casting core. Also, the dimensions of the casting core can be distorted and the casting core eroded when the core is blown around the plastic material. Further, this process is labor intensive. Thus, the need for improvements in such composite core assembly casting technology is present.